1. Field of the Invention
The invention relates to a system for bone segment navigation.
2. Discussion of Relevant Art
A system of this kind is known from U.S. Pat. No. 5,279,309 in which the position of the bone segment is sensed by means of markers which are arranged, at a spacing from the bone segment surface, on needles which penetrate into the bone segment surface.
However, this arrangement of the markers, constituted as light emitting diodes (LED), basically leaves open their exact spatial relationship to the bone segment or to a preoperative data set obtained by computerized tomography (CT). This can be obviated by producing the preoperative data set with the needles already inserted into the bone segment, but this of course makes necessary a surgical operation for setting the marker needles which precedes the bone segment displacement proper and which is stressful for the patient, and an additional, so-called planning CT, on which the marker needles are reproduced.
Another possible method of setting the markers in a spatial relationship to the bone segment, as also mentioned in U.S. Pat. No. 5,279,309, consists of sensing both the markers and also the bone segment with the tip of a feeler pin or pointer, the position of which can be measured by means of the position sensing unit. The spatial relationship of the markers relative to the bone segment can be established when, during the operation, unambiguously recognizable points both on the bone segment itself and also in the data set, so-called characteristic points, are touched and sensed according to position. However, the characteristic points then have to be touched and sensed according to position in a time-consuming manner during the operation. Furthermore, this has the precondition that such characteristic points exist.
This is of course not the case in many bone segments, so that the position determination of the bone segment itself as mentioned in U.S. Pat. No. 5,279,309 is not possible with the accuracy required in some cases of application.